The 12 volt side of life is one of the best resources for new RV'rs to read. Id' start there and them come back with any questions you have.
As for "turning it on" there are two different systems that need to be powered.
The first is the 12 volt side which runs off the battery or the converter when plugged into 120 volt power. The converter converts 120 volt AC into 12 volt DC. All your lights and some appliances run off 12 volts.
Next is the 120 volt side. It runs things like your A/C and powers the converter, it also runs the 120 volt side of your water heater if it has a 120 volt element.
To turn on the 120 volt side, you just need to plug the power cord of the RV into the power receptacle, then make sure the pedestal (or power receptacle) has power and that all the breakers in the RV are on. You should have 120 volt power then.
To turn on the 12 volt side, you need to make sure that all the fuses are good in the power center and that the battery disconnect is on if it has one.
In order to get the lights, etc. to work without shore power you'll need a good battery.